In the recovery of oil from subterranean formations it is frequently desirable to utilize some form of artificial lift in order to ensure the movement of oil from the producing formation to the surface at a commercially viable rate. One of the most widely used types of artificial lift apparatus is known as a downhole pump. In a typical downhole pump installation, a standing valve is mounted at the bottom of a tubing string and is provided with a check valve which permits fluid flow into the tubing only. A traveling valve is mounted for reciprocation within the tubing above the standing valve. The traveling valve is also provided with a check valve which permits fluid flow from the portion of the tubing extending between the traveling valve and the standing valve into the portion of the tubing extending above the traveling valve. The traveling valve is connected to the surface by a string of sucker rods. The uppermost sucker rod is in turn connected to the familiar pump jack.
Upon operation of the pump jack, the traveling valve is reciprocated within the tubing string. Reciprocation of the traveling valve causes fluid flow from the bottom of the well first through the standing valve into the portion of the tubing extending between the standing valve and the traveling valve, and then through the traveling valve into the portion of the tubing extending above the traveling valve. The upper portion of the tubing will eventually become filled with well fluid which permits recovery of the fluid at the surface.
The present invention relates to a hydraulically driven reciprocating motor. In accordance with the preferred embodiment of the invention, there is provided a hydraulically driven reciprocating motor which is adapted for use in lieu of a conventional pump jack in operating the traveling valve of a downhole pump. The primary advantage derived from the use of the invention involves the fact that by means thereof a motor for operating the traveling valve of a downhole pump can be manufactured and installed at considerably less cost than is possible when a conventional pump jack is used. Thus, in typical application, cost reductions of up to 75% or more may be realized when a hydraulically driven reciprocating motor incorporating the present invention is used instead of a conventional pump jack to operate the traveling valve of a downhole pump.
More specifically, the present invention comprises a hydraulically driven reciprocating motor including a hydraulic cylinder and a piston mounted for reciprocation within the cylinder. The piston has a passageway formed therethrough which is normally sealed by a floating valve. A rod is carried by the piston and normally projects from one end thereof. When the piston reaches the limit of its travel in one direction the rod disengages the floating valve, thereby opening the passageway through the piston to permit movement of the piston in the opposite direction. When the piston reaches the limit of its travel in the opposite direction the floating valve again seals the passageway through the piston to complete the operating cycle of the motor.